Anaïs (I would spell it this way) is my favourite of the two, although Anouk is super cute as well. I've always loved Anaïs Nin, she's one of my favourite writers, and the pefume Anaïs Anaïs was the first one I ever got, so these are very good associations for the name. Anaïs is not a version of Anna though, it's the French form of Anahita, an ancient Persian water/fertility goddess.